Dead Zones in Ocean

Dead zones in the ocean: "Every summer in the Gulf of Mexico, an area of the ocean up to the size of New Jersey loses its oxygen and almost everything in it dies. For its part, New Jersey suffers its own sea­sonal anoxia, as does Lake Erie, which saw the arrival of a toxic algae bloom so large in 2014 that it shut down the drinking supply for the city of Toledo. In 2016 the coast of Florida was battered by waves of thick, sea-life-smothering algal muck; boat owners described it as having the consistency of guacamole. The same kinds of problems afflict the greatly impoverished Chesapeake Bay, which up until relatively recently was a biological paradise. The Chesapeake once boasted oyster reefs so extensive as to rep­resent a navigational hazard to boats, as well as a menagerie of sea life that included 'dolphins, manatees, river otters, sea turtles, alligators, giant sturgeon, sharks and rays.' That roster might sur­prise modern pleasure boaters on the murky bay, where today one is about as likely to find a hippopotamus as a manatee. Farther afield, oxygen-poor waters beset the Baltic and East China Seas. This deadly phenomenon -- runaway algae growth robbing the seas of oxygen -- is called eutrophication. ...

Red circles show the location and size of many dead zones. Black dots show dead zones of unknown size.

"Eutrophication is caused by too much of a good thing -- an overdose of plant food. Today the Gulf of Mexico's problem starts in the heartland. When farmers in the endless rectangular patchwork of the Midwest and the Great Plains spread fertilizer rich in nitrogen and phosphorus on their crops, what isn't taken up by the plants is eventually washed into the Mississippi River. When the Mississippi empties into the ocean south of Louisiana, that accumulated Miracle-Gro spurs explosive algae growth in the open ocean. When the algae blooms die en masse, they sink and decompose, a process that uses up most of the oxygen in the water column. "Without oxygen, everything else suffocates, and the result is massive fish kills that make themselves known to Gulf Coast beachgoers in yearly biblical tides of lifeless stingrays, flounder, shrimp, eels, and fish. Underwater, dead crabs, clams, and bur­rowing worms litter the seabed like the casualties of an invertebrate Battle of the Somme. ... These algae blooms and dead zones around the world are spreading, driven by development and the growth of industrial agriculture."